Interpretive Summary: Macrophages are white blood cells that are critically important for the clearance of microorganisms from the body and in orchestrating an immune response. Normal macrophages are generally considered difficult or impossible to grow in vitro, i.e., in culture. A method for the culture of pig macrophages was presented. Pig macrophages were continuously cultured on feeder layers of STO mouse embryonic fibroblasts from explants of fetal pig testicle and liver tissue. The macrophages were characterized by light and electron microscopy, by their ability to ingest bacteria and by the detection of cell surface molecules known to be typical of macrophages. The pig macrophage cultures were maintained in culture for over 6 months and 30 population doublings. Macrophage cultures were also initiated from newborn and adult pig tissues. In addition, macrophages were grown from the embryonic tissues of the turkey, rat, mouse, cow and sheep, but these cultures were not characterized beyond light microscopic examination. Thi simple method of isolating and propagating tissue macrophages could routinely provide normal macrophages for research proposes, such as AIDS research, and might also provide macrophages for adoptive immunotherapy and somatic gene therapy.

Technical Abstract:
Normal tissue macrophages from fetal and adult pig tissues can be continuously cultured by growing simple explant cultures on feeder layers of STO mouse embryonic fibroblasts. Macrophage cultures initiated from fetal and newborn pig testicle and liver explants grew from eight to 30 population doublings. The macrophages grew on top of the STO feeder cells in two forms: either a semi-attached round, refractile morphology, or a closely attached ameboid morphology with several extended pseudopods. Cultured macrophages had large lobed nuclei, numerous complex vacuoles, and filopodia by transmission electron microscopic examination. The macrophages rapidly took up and sequestered acetylated-LDL in their vacuoles. They were highly phagocytic and expressed CD14 on their surface. Macrophage cultures were also initiated from tissues of the turkey, rat, mouse, cow, and sheep (data not shown). This simple method of isolating and propagating tissue macrophages could routinely provide macrophages for general research, adoptive immunotherapy, and somatic gene therapy.